﻿//Copyright (c) 2009, Offbeat Guides
//All rights reserved.
//
//Redistribution and use in source and binary forms, with or without modification, are 
//permitted provided that the following conditions are met:
//
//* Redistributions of source code must retain the above copyright notice, this list of 
//conditions and the following disclaimer.
//
//* Redistributions in binary form must reproduce the above copyright notice, this list 
//of conditions and the following disclaimer in the documentation and/or other materials 
//provided with the distribution.
//
//* Neither the name of Offbeat Guides nor the names of its contributors may be used to 
//endorse or promote products derived from this software without specific prior written 
//permission.
//
//THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY 
//EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 
//OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT 
//SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
//SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 
//OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
//HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR 
//TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 
//EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Cryptography;

namespace Amazon.Services
{
    internal static class OAuth
    {
        #region Static Variables
        private static readonly System.Text.Encoding DefaultEncoding = new UTF8Encoding();
        #endregion

        #region Methods
        public static String GenerateSignature(IServiceConfiguration configuration, String method, String key, IDictionary<String, String> parameters)
        {
            KeyedHashAlgorithm algorithm = new HMACSHA1();
            String data = null;
            switch (configuration.SignatureVersion)
            {
                case "0":
                    data = OAuth.CalculateStringToSignV0(parameters);
                    break;
                case "1":
                    data = OAuth.CalculateStringToSignV1(parameters);
                    break;
                case "2":
                    if (!parameters.ContainsKey("SignatureMethod"))
                        parameters.Add("SignatureMethod", configuration.SignatureMethod);

                    algorithm = KeyedHashAlgorithm.Create(configuration.SignatureMethod);
                    data = OAuth.CalculateStringToSignV2(configuration.ServiceUrl, method, parameters);
                    break;
                default:
                    throw new Exception("Invalid Signature Version specified");
            }

            algorithm.Key = OAuth.DefaultEncoding.GetBytes(key);
            Byte[] buffer = OAuth.DefaultEncoding.GetBytes(data.ToCharArray());
            buffer = algorithm.ComputeHash(buffer);
            return Convert.ToBase64String(buffer);
        }

        private static String CalculateStringToSignV0(IDictionary<String, String> parameters)
        {
            return String.Format("{0}{1}", parameters["Action"], parameters["Timestamp"]);
        }

        private static String CalculateStringToSignV1(IDictionary<String, String> parameters)
        {
            IDictionary<String, String> sortedParameters = new SortedDictionary<String, String>(parameters, StringComparer.OrdinalIgnoreCase);

            StringBuilder parameterValues = new StringBuilder();
            foreach (KeyValuePair<String, String> pair in sortedParameters)
            {
                if (pair.Value != null)
                    parameterValues.AppendFormat("{0}{1}", pair.Key, pair.Value);
            }

            return parameterValues.ToString();
        }

        private static String CalculateStringToSignV2(String serviceUrl, String method, IDictionary<String, String> parameters)
        {
            IDictionary<String, String> sortedParameters = new SortedDictionary<String, String>(parameters, StringComparer.Ordinal);

            Uri endpoint = new Uri(serviceUrl.ToLower());
            String uri = String.IsNullOrEmpty(endpoint.AbsolutePath) ? "/" : endpoint.AbsolutePath;

            StringBuilder parameterValues = new StringBuilder();
            foreach (KeyValuePair<String, String> pair in sortedParameters)
            {
                if (pair.Value != null)
                    parameterValues.AppendFormat("{0}={1}&", Utility.UrlEncode(pair.Key), Utility.UrlEncode(pair.Value));
            }

            return String.Format("{0}\n{1}\n{2}\n{3}",
                method,
                endpoint.Host,
                Utility.UrlEncode(uri).Replace("%2F", "/"),
                parameterValues.Remove(parameterValues.Length - 1, 1).ToString());
        } 
        #endregion
    }
}
